A rotary pump is known from DE-A-33 16 927 that is comprised of a housing divided into two identical housing halves by a plane that is located perpendicular to the housing axis and running through the middle of the housing and is preferably made of plastic. The housing has a separately-formed outlet pipe that is connected to a lateral outlet opening provided on the external periphery of the housing. In one embodiment of the housing, the direction of its outlet opening is offset to the center axis of the housing. In addition, the interior chamber of the pump housing extends into the connection area of the outlet pipe. The outlet opening of the housing is provided with a flange, so that the outlet pipe can be mounted on the bearing surface of the housing with a corresponding rectangular connection flange. The rotary pump is adapted to various requirements through the use of outlet pipes of corresponding different shapes. The two-part embodiment of the housing with identical housing halves, which has an opening for securing to a pump or to receive a cover with an inlet opening, restricts the usable area. For ease of assembly, the impeller may not be larger than said opening. Consequently, the pump has an impeller diameter that is much smaller than the diameter of the housing, and adjustment of its power is restricted with regard to delivery heads and flow rates. The rotary pump shown in the illustration is a non-clogging pump used to convey high flow rates of contaminated water containing a great deal of grease. Therefore, the pump is not intended for the build-up of high pressures. Furthermore, this design has the disadvantage that many parts must be assembled. In addition to the housing parts, seals and connecting elements are required. The way in which the parts are connected requires flanges, and gaps in which deposits can form are produced between the parts.
DE-A-30-00 095 shows a centrifugal pump having a pump housing that has a discharge disposed substantially tangentially in relation to the wall enclosing the pump housing, whereby the discharge has an opening with a substantially rectangular cross section. That opening diminishes the stiffness of the housing and does not provide any additional protection against the deformation forces caused by the internal pressure. Welding to the pipe is difficult, since the welded seam runs in three planes. For that reason, the pipe is designed in such a way that it can be mounted on the three-dimensional contour of the housing.